Rights groups say she had shouted slogans against the Chinese government before self-immolating on Saturday.

At least 20 Tibetans have reportedly self-immolated over the last year.

According to rights groups, the nun was from the Mamae nunnery, which has a reputation for being loyal to Tibetan spiritual leader, the Dalai Lama. Xinhua reported that she died on the way to the hospital on Saturday evening.

"Soldiers surrounded the nunnery and sealed it off, and nothing more is known of the situation inside," Kanyag Tsering, a monk based in Dharamsala, India, where the Tibetan government-in-exile is based, was quoted by the Reuters news agency as saying.

The Tibet Divide

China says Tibet always part of its territory

Tibet had long periods of autonomy

China launched a military assault in 1950

Opposition to Chinese rule led to a bloody uprising in 1959

Dalai Lama fled to India

Most of the cases of monks and nuns setting themselves alight have been in Aba county, an ethnic Tibetan area of Sichuan. The Tibetan-populated parts of China are experiencing their worst unrest in four years, ahead of the Tibetan new year on 22 February.

Chinese authorities have recently launched a major security operation to try and end the unrest.

On 9 February, it was reported that four officials in the regional government were sacked for "endangering stability", after the government earlier warned that they had to maintain order or face dismissal or criminal charges.

The incident follows a series of deadly protests against Chinese rule in the province since January. Last month, three protests were also reported.

International media are denied access to the area, making it difficult to verify accounts.